1. Field of the Invention
This invention relates to fiber-reinforced concretes. More particularly, it relates to composite materials obtained by uniformly dispersing short fibers in mortars or concretes and also to reinforcing materials, i.e. short fibers to be incorporated in the concrete.
2. Description of the Prior Art
It is known to incorporate or disperse in concretes a reinforcing material such as steel fibers in order to improve tensile and flexural strengths of the concrete. Such a technique has been already disclosed in U.S. Pat. No. 3,953,953 and the reinforced concretes have been practically used as a paving material or a lining of tunnel because of their excellent characteristics. The fiber-reinforced concretes are incorporated ensure higher crazing and maximum loads as compared with ordinary concretes but have a drawback that high toughness can not be expected since the impartment of toughness is dependent on whether the short fiber is easily withdrawn from a concrete matrix.
It is also known that when a reinforcing material of a synthetic plastic fiber is incorporated in concrete, the concrete can stand against a fairly great degree of deformation and is remarkably improved in toughness such as disclosed in British Pat. No. 1,305,206. But they have a drawback in that the craze resistance is small, i.e. an initial yield strength or proof stress is small.
Compare also British Patent Specification No. 1,406,442 featuring "a mix for making reinforced concrete comprising cement, sand, aggregate, strands formed of at least two fibres twisted together and/or individual fibres and water, the strands and/or fibres being of various lengths and cross-sectional dimensions."